This encryption is only used in Telegram's calls and 'secret conversations' functionality, not in regular chats. Those are solely encrypted client-server communications. Telegram's increased cloud usage. It basically saves all of your chats and photos on a safe server. Telegram is significantly more multi-platform friendly than other chat apps like WhatsApp because you may access them from any connected device.
Usernames are another security element that improves usability. You can just give your username to folks instead of your phone number. This allows you to have more control over what information is publicly available and how individuals can contact you in the future.